Please read for an updated status on RailsCasts:
Learn more or hide this
GitHub User: ano1chan
A painful memory while you are exporting 50K above of row in SpreadsheetML
And this occupy one of the worker while in production.
Even you finish export with SpreadsheetML, your customer may can't open it because it is too big and eat up the memory in excel.
I end up writing a rake task and put that in background with spreadsheet gem.
Smaller output and better user experience.
May be I am doing it wrong but that's my experience.